1. Field of the Invention
The present invention relates to a developing apparatus for use in a copying machine, a printer, a facsimile and the like. More particularly, it relates to a developing apparatus having a sealing mechanism for preventing the leakage of toners therefrom.
2. Description of the Related Art
Heretofore, a developing apparatus as shown in FIGS. 1 and 2 is proposed.
According to the developing apparatuses, a driving roller 3 is disposed in front of a developing tank 2 and a thin film sleeve 4 is mounted around the driving roller 3.
The thin film sleeve 4 is made of a resin sheet such as polyester or a thin metal film and the outer surface thereof is roughened by blast treatment. Its circumference is longer than that of the driving roller 3.
As shown in FIG. 2, a sealing member 5 disposed between the thin film sleeve 4 and a developing tank 2 is pressed against both end portions of the thin film sleeve 4 forward so that toners held by the thin film sleeve 4 on the surface thereof is prevented from dropping from both end portions thereof and the thin film sleeve 4 closely contact with the peripheral surface of the driving roller 3 so as to loosen the thin film sleeve 4 in the front thereof. As a result, a space (S) is formed between the thin film sleeve 4 and the driving roller 3 in the region in which the thin film sleeve 4 confronts an electrophotoreceptor drum 20. The space between the bottom of the thin film sleeve 4 and the developing tank 2 is also sealed. A regulating plate 8 for regulating the amount of toners to be supplied to the thin film sleeve 4 is disposed in the rear of the thin film sleeve 4. A scraper rod 9 is mounted on the regulating plate 8 in the vicinity of the bottom thereof so that the scraper rod 9 is pressed against the thin film sleeve 4.
Supposing that the friction coefficient between the thin film sleeve 4 and the driving roller 3 is .mu..sub.1 and the friction coefficient between the thin film sleeve 4 and the sealing member 5 is .mu..sub.2, the following relationship is established: .mu..sub.1 &gt;.mu..sub.2.
Agitating blades 15 and 16 are disposed in a toner accommodating section 14 disposed rearward of the developing tank 2.
In the developing apparatus 1 having the above-described construction, toners accommodated in the toner accommodating section 14 are transported toward the thin film sleeve 4 due to the rotations of the agitating blades 15 and 16 in the direction shown by arrows. The driving roller 3 rotates in the direction shown by an arrow (a), which causes the thin film 4 to rotate in the direction shown by the arrow (a). In the toner accommodating section 14, part of toners held by the thin film sleeve 4 on the peripheral surface thereof are scraped by the scraper rod 9. Consequently, toners which have passed between the scraper rod 9 and the thin film sleeve 4 are electrified and form a layer of a uniform thickness.
When the electrified thin layer of toners are transported by the thin film sleeve 4 to the area in which the thin film sleeve 4 confronts the electrophotoreceptor drum 20, toners are supplied to an electrostatic latent image formed thereon.
In the developing apparatus 1 shown in FIG. 2, both end faces of the scraper rod 9 only contact with the inner peripheral surface of the sealing member 5. Thus, the sealing performance of the sealing member 5 is incomplete. Accordingly, the large amount of toner passes, in a direction indicated by an arrow (X), between the end faces of the scraper rod 9 and the inner peripheral surface of the sealing member 5 and adheres to the electrophotoreceptor drum 20 so that a fog occurs on a developed image or toners drop from the developing apparatus, thus soiling the inside of the copying apparatus.
Further, toners scraped by the scraper rod 9 drop therefrom and penetrate into the contact face between the thin film sleeve 4 and the sealing member 5, thus falling from the developing apparatus 1 or penetrating into the contact face between the driving roller 3 and the thin film sleeve 4 in the direction shown by an arrow (Y). Consequently, the driving roller 3 and the thin film sleeve 4 slip from each other and toners adhere to a bearing or a gear, which causes the unstable driving of the developing apparatus.
In order to solve the above-described problem, the sealing member 5 may be pressed against the thin film sleeve 4 in a greater force so as to prevent toners from penetrating into the contact face between the thin film sleeve 4 and the sealing member 5, but a greater torque for rotating the driving roller 3 is required. In addition, this method is incapable of completely preventing toners from penetrating therebetween.
Still further, in the above-described developing apparatus, it is necessary that the thin film sleeve 4 is pressed against the driving roller 3 in a constant force so that the thin film sleeve 4 is rotated in a constant speed by the driving roller 3.
To this end, an elastic pad made of, for example, urethane foam may be provided in the rear of the thin film sleeve 4 and the elastic pad is sandwiched between the developing tank 2 and the driving roller 3 on which the thin film sleeve is mounted. According to this construction, the thin film sleeve 4 is pressed against the driving roller 3 by the elastic rebound of the elastic pad. But the elastic rebound of the elastic pad is reduced with the elapse of time, so that toners leak through the face between the elastic pad and the thin film sleeve 4 which rotates in contact with the elastic pad and a sufficient friction force is not generated between the thin film sleeve 4 and the driving roller 3.
If the elastic pad is composed by jointing elastic pads which contact with the peripheral surfaces of both ends of the thin film sleeve 4 with an elastic pad which connect the elastic pads, toners may leak through the joints.